The present invention relates to a method for monitoring state of health of a vehicle system over the life time of the vehicle, and further to a computer program and a computer program product for performing such a method.
Vehicles and vehicle components are tested during manufacture of the vehicle. Most components can be tested and verified at the sub-supplier when the component is manufactured. However, many components are comprised in a system in which several different components make up the system. Such a system can only be tested and verified when completely assembled. Some system can only be tested and verified when mounted on the vehicle, since they require input from other systems.
Even if each component that is comprised in a system is verified and complies with the required tolerances, the system itself may still be out of tolerance due to added tolerances from the different components. Thus, with normal deviation, some systems may be out of tolerance. In a vehicle, with several different sub-systems, it is likely that some vehicles will perform somewhat differently than other vehicles, where the added tolerances will compensate each other. Some vehicles may even perform much better than the average vehicle when the tolerances are added in an optimal way.
Normally, each component or system has to comply with a given tolerance. Such tolerances are decided upon such that most components and systems will function properly, but are fixed values that can be compared with measured values for the component or system. A component that falls outside a fixed tolerance value is discarded, even if the component could function properly with other components adapted for that measure. Also complete systems of a vehicle will have to be within certain fixed tolerances.
If a component or system is close to a tolerance limit, it will be within tolerance. When the component or system has been used for a while, it may fall outside the tolerance limit due to wear, even if the component or system is not worn very much. In an inspection, the component or system may thus be seen as defective.
Some components and systems have greater deviations than other. It is e.g. fairly easy and cost-effective to manufacture valves within tight tolerances, but more difficult or impossible to manufacture an electrical component within a specified tolerance. The only way to arrive at a required tolerance may then be to manufacture several components and to thereafter measure all components and to group them in different component classes having different tolerances. This is a costly and time-consuming operation. Further, this grouping may only be valid when the component is new, since different components may age differently. Even if a new component was within tolerance, it may be seen as out of tolerance when measured after use.
Some components or systems may also be mounted on the vehicle and may thereafter be adjusted to a specific tolerance. This applies to certain electrical components and systems, where a calibration is done after mounting.
Some components and systems will have a predicted ageing behaviour, which can be used to determine when a service or replacement is to be performed on that component or system. One disadvantage of using a predicted ageing for a component or a system is that some components or systems may be unnecessarily serviced or replaced. Other components or systems may not be serviced or replaced in time, due to a higher wear than predicted.
It is thus room for an improved method for monitoring state of health of a vehicle system over the life time of the vehicle.
It is desirable to provide an improved method for monitoring state of health of a vehicle system.
In a method for monitoring state of health of a vehicle system, the steps of measuring a plurality of parameter values for the system at different running conditions as an end of line test, storing the parameter values in a fingerprint file, measuring the same plurality of parameter values that is comprised in the fingerprint file after a predefined time interval, adding a predefined ageing offset to the fingerprint file, where the ageing offset corresponds to a predicted wear of the system during the predefined time interval, thereby obtaining a time modified fingerprint file for the system, comparing the measured values with the time modified fingerprint file, and issuing a message if the measured values deviates from the time modified fingerprint file are comprised.
By this first embodiment of the method, the method can monitor the state of health of a vehicle system, and determine if the state of health is within predefined limits or not. This is done by first measuring a plurality of parameter values for the specific system when the system of the vehicle is new, e.g. as an end of line test at the manufacturing plant. The parameters are measured at different running conditions, e.g. at different load conditions such as at low load, medium load and top load. The parameter values for the different load conditions are stored in a fingerprint file that is saved in a memory in the vehicle control system. This original fingerprint file will thus contain the actual performance of the system when it was delivered. The same parameters are measured at similar load conditions at a later moment, and are stored in an additional fingerprint file. Similar load conditions may either be simulated in e.g. a work shop when the vehicle stands still, or may be found when the vehicle travels on a road. The acceleration of a fully loaded vehicle will e.g. correspond to a full load condition, and a slow marshalling will e.g. correspond to a low load condition. Since the different measurements are stored in an additional fingerprint file, where the measurements are confined by an acceptance area, it is not important that the different load conditions are exactly the same. It is still important that measurements are measured at different load conditions.
Further, an ageing offset is added to the original, fingerprint file and stored in a modified fingerprint file. The ageing offset comprises a predefined ageing behaviour of the system, and is dependent on time or travelled distance of the vehicle. The measured values contained in the additional fingerprint file are compared with the modified fingerprint file. If the measured values, i.e. the additional fingerprint file, deviate from the modified fingerprint file, a message is issued. The message may be given to the operator of the vehicle or may be saved in an error log of the vehicle, where a work shop can investigate the cause at a later stage, or at a regular service appointment.
In a development of the method, the moment when the additional fingerprint file is measured corresponds to a regular service interval. In this way, the measurements of the plurality of parameters may be performed at the work shop, in a controlled environment. In a work shop, it is easier to perform the different measurements at the same conditions as for the end-of-line test, since the same conditions can easily be simulated at stand still. For some measurements, it may be advantageous to use an artificial, simulated load instead of a real load. One such load may be art engine load, where it may be easier to simulate a top load condition in a work shop than to find such a condition on the road.
An additional fingerprint file is measured at different time intervals. The time intervals may either be predefined time intervals, where a time interval may be a month or more, or may be based on travelled distance of the vehicle. It is of course also possible to measure additional fingerprint files at other moments, such as at shorter time intervals, but since the ageing of the systems are normally relatively slow, such that it may take several years until a critical degradation has occurred, a month or more suffice. It is also possible to initiate an additional fingerprint measurement from a service centre, in order to obtain an additional fingerprint file for a specific system or component.
The additional fingerprint files may also be saved in a memory, such that a statistical follow up can be made. The additional fingerprint files may be stored in the vehicle control system or may be transferred to a central data base at the manufacturer. An advantage of storing the additional fingerprint files at the manufacturer is that the manufacturer can use the collected additional fingerprint files from several different vehicles in order to perform follow up investigations on different components that have been found faulty or that have been redesigned.
The vehicle is preferably a hybrid vehicle comprising a combustion engine and an electric engine powered by a battery or other electrical power source. The vehicle system may be e.g. a diesel engine, an electric engine, an exhaust after treatment system, a cooling system or a battery. The ageing offset may be dependent on outer conditions of the vehicle, such as temperature, altitude, humidity, geographical position or the number of particles in the air. The ageing offset may also be dependent on the distance travelled by the vehicle.
In a development of the method, at least two additional fingerprint flies may he combined in a fingerprint matrix. In this development, several original fingerprint files are combined into an original fingerprint matrix comprising measurements from the end-of-line test. After a predefined time interval, several additional fingerprint files are measured and subsequently combined into an additional fingerprint matrix, which is compared with the original fingerprint matrix. A message is issued if the additional fingerprint matrix deviates from the original fingerprint matrix. An advantage of using a fingerprint matrix is that several systems can be compared at the same time, and that the relation between different systems can be compensated for directly in the matrix. In this way, the comparison can take account of different relationships in an easy way.